Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a canister. During a subsequent engine operation, the stored vapors can be purged into the engine for combustion. Various approaches may be used to generate vacuum for drawing the fuel vapors into the engine. For example, an intake manifold vacuum generated during engine spinning can be used to draw in the stored fuel vapors. However, during conditions when intake manifold pressure is at or above atmospheric conditions (e.g., during boost conditions in a turbocharged engine), an amount of vacuum available in the intake manifold for purging may be reduced, which may lead to incomplete purging and degraded emissions.
In some approaches for providing vacuum for fuel vapor purging to supplement intake manifold vacuum, active or passive vacuum pumps are used to generate vacuum. For example, as shown by Kempf et al. in U.S. 2013/0263590, an ejector which harnesses the venturi effect to generate vacuum may draw stored fuel vapors into an entraining inlet while motive flow passes from a motive inlet to a mixed flow outlet thereof. In this way, stored fuel vapors may be pumped by the ejector from the fuel vapor canister to the engine intake passage.
However, the inventors herein have recognized that in approaches wherein an outlet of a conventional canister purge valve is coupled to a suction port of a passive vacuum pump such as an ejector, the flow restriction present in a conventional canister purge valve may negatively affect performance of the ejector (e.g., by decreasing ejector suction flow rate). For example, while conventional canister purge valves include a flow restriction in close proximity with a solenoid valve to reduce the solenoid force required to actuate the valve, the presence of the flow restriction causes flow exiting the canister purge valve and entering the suction port of an aspirator to undergo two restrictions (e.g., the flow restriction in the canister purge valve and then the flow restriction at the suction port of the aspirator).
In one example, the issues described above may be addressed by vehicle system which includes an ejector in a compressor recirculation passage, an aspirator in a throttle bypass passage, and further includes a canister purge valve having first and second outlets. A single flow restriction may be arranged in a first passage of the canister purge valve coupling a solenoid with the first outlet leading to an intake manifold, while a second passage of the canister purge valve which has no flow restriction may couple the solenoid with the second outlet which leads to a suction port of the ejector. In this way, by providing a path from the fuel vapor purge system to ejector suction port which does not include any flow restrictions, a higher rate of suction flow into the ejector may be achieved relative to configurations wherein fuel vapor purge gases undergo a flow restriction within the canister purge valve before entering an ejector suction port.
Further, a common shut-off valve, or a pair of shut-off valves actuated by a common actuator, may serve to direct intake air from downstream of a turbocharger compressor into one or both of the compressor recirculation path and throttle bypass passage to provide motive flows for the ejector and/or aspirator. Utilizing a common shut-off valve or a commonly-actuated pair of shut-off valves may advantageously reduce costs. For example, the inventors have recognized that it may be advantageous to direct flow into the compressor recirculation flow path during boost conditions (e.g., to generate ejector vacuum while mitigating compressor surge), whereas it may be advantageous to direct flow into the throttle bypass flow path during conditions where intake manifold vacuum is relatively low (e.g., conditions where intake manifold pressure is relatively high, such as boost conditions). Accordingly, it may be advantageous to utilize a common shut-off valve to simultaneously enable both compressor recirculation flow and throttle bypass flow, in some examples.
The technical effect of omitting a flow restriction in a flow path between the fuel vapor purge system and an inlet of an ejector which generates suction to induce fuel vapor purging is that a higher suction flow rate (and thus a higher purge flow rate) may be achieved, even at relatively low boost levels (e.g., when motive flow through the ejector is relatively low).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.